GPR3 activates adenylate cyclase in the absence of ligand.[3] GPR3 is expressed in mammalian oocytes where it maintains meiotic arrest and is thought to be a communication link between oocytes and the surrounding somatic tissue.[4] It has been proposed that sphingosine 1-phosphate (S1P) and sphingosylphosphorylcholine (SPC) are GPR3 ligands,[5][6] however this result was not confirmed in a β-arrestin recruitment assay.[7]